Aluminoborosilicate glass

ABSTRACT

An aluminoborosilicate glass having a density less than 2.40 g/cm 3  and a specific modulus of elasticity greater than 30 GPa·cm 3 ·g −1  is disclosed that comprises the following components (in wt. %): SiO 2  58-70, Al 2 O 3  12-20, B 2 O 3  5-15, MgO 0-9, CaO 2-12, BaO 0,1-5, SnO 2  0-1, As 2 O 3  0-2, the glass, apart from random impurities, being free of SrO and free of alkali oxides. The glass is particularly suitable as a substrate glass for LCD displays, for example.

RELATED APPLICATIONS

This application claims priority of German patent application 10 2006 016 256.0, filed on Mar. 31, 2006, the contents of which are fully incorporated by reference herein.

BACKGROUND OF THE INVENTION

The invention relates to an aluminoborosilicate glass having a particularly low density and a high specific modulus of elasticity, and to advantageous uses of such a glass.

LCD displays are becoming increasingly widespread, not only as computer screens but also as large-format flat screens. TFT-LCD displays (active matrix thin-film transistor LCDs), especially, have low power consumption and are therefore used in many applications, for example in notebooks, in flatscreens, in digital cameras and the like. The display substrate usually consists of a glass plate in each case.

Such substrates must meet high standards. In addition to high thermal shock resistance and good resistance to the aggressive chemicals used in the production of flat screens, the glasses should also have a wide spectral range (VIS, UV), high transparency, and a low density in order to save weight. Furthermore, using them as a substrate material for integrated semiconductor circuitry, for example in TFT displays, requires that they be thermally adapted to the silicon thin-film material. When largely crystalline silicon layers are produced by high-temperature treatment at temperatures above 700° C., or by direct deposition in CVD processes, a substrate is required which has a low thermal expansion coefficient of less than 3.2·10⁻⁶/K, if possible. Another condition for applications in the field of display and photovoltaics technology is the absence of alkali ions. Sodium oxide concentrations of below 1000 ppm resulting from production-related factors are still tolerable with regard to the “poisoning” effect resulting from the diffusion of Na⁺ into the semiconductor layer.

However, for use in large-format displays, it is particularly essentially that the substrate has a high elasticity modulus, a low density and a high specific modulus of elasticity.

It is also desired that suitable glasses can be commercially produced in a cost-efficient manner and at a sufficient level of quality (no bubbles, knots or occlusions), for example in a float glass plant or in a down-draw process. The production in drawing processes of thin (<1 mm), streakless substrates of low surface waviness, especially, requires that the glass have a high devitrification stability. In order to counteract any disadvantageous compaction of the substrate on the semiconductor microstructure during production, particularly in the case of TFT displays, the glass also needs to have a suitable temperature-dependent viscosity curve. This means that, as far as its thermal process and form stability are concerned, it should have a viscosity in the melting and processing range which is not too high, yet also have a sufficiently high transformation temperature, i.e. T_(g)≧700° C.

Many glasses used especially for displays such as LCDs and TFT-LCDs are described in the prior art.

A number of alkali-free aluminoborosilicate glasses are known from WO 02/060831 which have a relatively low density of less than 2.4 g/cm³ in some cases, but a specific modulus of elasticity that is always below 30 GPa·g⁻¹·cm³.

Other alkali-free aluminoborosilicate glasses are known from DE 100 00 836 A1, but these all have a density greater than 2.4 g/cm³, which is considered disadvantageous in portable applications, especially, such as notebooks.

A number of other aluminoborosilicate glasses for such applications and which have a high modulus of elasticity and a high specific modulus of elasticity are known from U.S. Pat. No. 6,537,937 B1.

However, the transformation temperature of these glasses is less than 700° C. in all cases, which is considered disadvantageous.

Other glasses of a similar kind are known from U.S. Pat. No. 5,851,939; U.S. Pat. No. 6,060,168; DE 100 64 804 A1; U.S. Pat. No. 6,319,867 B1; EP 0 672 629 A2; DE 196 80 967 T1; JP 2004-91244 A; and from JP 08-295530 A.

However, all of these fail to meet the requirements referred to at the beginning.

SUMMARY OF THE INVENTION

It is a first object of the invention to disclose an alkali-free alumino-borosilicate glass that has a low a density and a high specific modulus of elasticity.

It is a second object of the invention to disclose an alkali-free alumino-borosilicate glass that is particularly suitable for use in the production of displays, especially, such as LCD displays.

It is a third object of the invention to disclose an alkali-free alumino-borosilicate glass that has a viscosity characteristic that is optimized for the manufacture of displays.

According to the invention these and other objects are accomplished by an aluminoborosilicate glass having a density less than 2.40 g/cm³ and a specific modulus of elasticity less than 30 GPa·cm³·g⁻¹ and comprising the following components (in wt. %): SiO₂ 58-70  Al₂O₃ 12-20  B₂O₃ 5-15 MgO 0-<6 CaO 2-12 BaO 0.1-5   SnO₂ 0-1  As₂O₃ 0-2, 

the glass, apart from random impurities, being free of SrO and free of alkali oxides. Preferably, aside from random impurities, no other components are contained in the glass.

It has been found that, by adding barium oxide in the simultaneous absence of strontium oxide, a very low density can be achieved, on the one hand, as well as a high specific modulus of elasticity, on the other hand. The special requirements in respect of the viscosity curve and a high transformation temperature are also fulfilled.

Surprisingly, a low density of less than 2.4 g/cm³ is obtained, despite the presence of barium oxide, which helps in turn to achieve a high modulus of elasticity and a high specific modulus of elasticity.

In a preferred development of the invention, the calcium oxide content is less than 6 wt.-%, but is at least 4 wt.-%.

The magnesium oxide content is preferably more than 0.5% because this likewise increases the modulus of elasticity. The meltability is also increased by the addition of MgO, in that the viscosity of the glass at 10⁴ dPas (referred to as VA), is reduced by higher concentrations of magnesium oxide.

However, the magnesium oxide content should not exceed 6 wt.-%.

According to another development of the invention, the B₂O₃ content is less than 14 wt.-%.

Since the glass is preferably free of strontium oxide and free of alkali oxides, the strontium oxide content should be less than 0.1 wt. % and preferably less than 0.02 wt. %. The alkali oxide content is preferably less than 0.1 wt. % and preferably less than 0.02 wt. %.

The glasses according to the invention preferably have a specific modulus of elasticity which is greater than 31 GPa·cm³·g⁻¹ and preferably greater than 32 GPa·cm³·g⁻¹.

In addition, the glasses according to the invention preferably have a modulus of elasticity which is greater than 71 GPa, preferably more than 73 GPa, and it is particularly preferred that the modulus of elasticity is greater than 75 GPa.

The viscosity temperature at 10⁴ dPas of the glasses according to the invention is preferably less than 1320° C., and the viscosity temperature at 10² dPas is preferably less than 1690° C.

The glasses according to the invention preferably all have a transformation temperature T_(g) of at least 700° C.

The glasses according to the invention are suitable preferably as substrate glasses, especially for OLEDs, AMOLEDs (active matrix OLEDs), FEDs (field emission displays), SEDs (surface emission displays), as filter glass, in particular as color filter glass, or as color glass.

The glasses according to the invention are also suitable for LCD-TFT displays, in particular, for displays with backlighting of flat screen displays in non-self-emitting systems, in particular as flat glasses for FFLs (flat fluorescent lamps), particularly for EEFL (external electrode fluorescent lamp) systems with external electrodes.

Within this context, the dielectric properties of the glass acquire special importance. The glasses according to the invention have a low tanδ/ε′ quotient (dielectric loss angle/dielectric constant).

The glasses according to the invention can preferably be produced by the float process. The glasses according to the invention glasses are also suitable for a production process using the down-draw process and in particular using the overflow fusion process.

It is self-evident that the features of the invention as mentioned above and to be explained below can be applied not only in the combination specified in each case, but also in other combinations or in isolation, without departing from the scope of the invention.

Additional features and advantages derive from the following description of preferred embodiments.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT EXAMPLE

The glasses according to the invention preferably have the following composition (in wt. %): SiO₂ 58-65  Al₂O₃ 15-18  B₂O₃ 8-12 MgO 0.5-5   CaO 4-<6 BaO 0.1-2   SnO₂ 0-1  As₂O₃ 0-2. 

Table 1 shows the composition of glass (Example 1) according to the invention and its characteristic properties. Table 1 also shows, as comparative example V1, a glass that does not belong to the invention which is free of barium oxide and contains strontium oxide instead. It is found that, although this comparative example V1 has a density less than 2.4 g/cm⁻³, the specific modulus of elasticity is less than 30 GPa·cm³·g⁻¹.

The glass according to the invention has a barium oxide content of 1.0 wt. %, is free of strontium oxide (and alkali oxides) and has a specific modulus of elasticity greater than 30 GPa·cm³·g⁻¹, and a density less than 2.4 g·cm⁻³. Furthermore, the transformation temperature T_(g) of the glasses according to the invention glasses is more than 710° C., whereas the temperature when the viscosity of the glasses is 10⁴ dPas is less than 1320° C., and the viscosity temperature at 10² dPas is less than 1670° C. The coefficient of thermal expansion, at 3.11·10⁻⁶/K, is also in a preferred range. TABLE 1 Example Composition (wt.-%) 1 V1 SiO₂ 63.40 63.7 Al₂O₃ 16.90 16.1 B₂O₃ 9.90 10.3 MgO 2.80 0.2 CaO 5.90 7.8 BaO 1.00 — SnO₂ 0.20 — As₂O₃ — 1.1 α (10⁻⁶/K) (20-300° C.) 3.11 3.21 T_(g) (° C.) 719 716 κ (kg · m⁻³) 2394 2367 T₄ (° C. at 10⁴ dPas) 1312 1330 T₂ (° C. at 10² dPas) 1678 1717 Modulus of elasticity (GPa) 79 70 Specific modulus of elasticity 33.0 29.4 (GPa · cm³ · g⁻¹) 

1. An aluminoborosilicate glass having a density less than 2.40 g/cm³ and comprising the following components (in wt. %): SiO₂ 58-70 Al₂O₃ 12-20 B₂O₃  5-15 MgO 0-9 CaO  2-12 BaO 0.1-5   SnO₂ 0-1 As₂O₃  0-2,

said glass, apart from random impurities, being free of SrO and free of alkali oxides; said glass further having a specific modulus of elasticity greater than 31 GPa·cm³·g⁻¹, a modulus of elasticity greater than 71 GPa, a viscosity temperature of less than 1320° C. at 10⁴ dPas, and a viscosity temperature of less than 1670° C. at 10² dPas.
 2. The aluminoborosilicate glass of claim 1, in which the modulus of elasticity is greater than 75 GPa.
 3. The aluminoborosilicate glass of claim 2, in which the specific modulus of elasticity is greater than 32 GPa·cm³·g⁻¹.
 4. The aluminoborosilicate glass of claim 3, having a transformation temperature T_(g) of at least 710° C.
 5. An aluminoborosilicate glass having a density less than 2.40 g/cm³ and a specific modulus of elasticity greater than 30 GPa·cm³·g⁻¹ and comprising the following components (in wt. %): SiO₂ 58-70 Al₂O₃ 12-20 B₂O₃  5-15 MgO 0-9 CaO  2-12 BaO 0.1-5   SnO₂ 0-1 As₂O₃  0-2,

said glass, apart from random impurities, being free of SrO and free of alkali oxides.
 6. The aluminoborosilicate glass of claim 5, in which the specific modulus of elasticity is greater than 31 GPa·cm³·g⁻¹.
 7. The aluminoborosilicate glass of claim 5, in which the specific modulus of elasticity is greater than 32 GPa·cm³·g⁻¹.
 8. The aluminoborosilicate glass of claim 5, in which the modulus of elasticity is greater than 71 GPa.
 9. The aluminoborosilicate glass of claim 8, in which the modulus of elasticity is greater than 73 GPa.
 10. The aluminoborosilicate glass of claim 5, having a viscosity temperature less than 1320° C., at 10⁴ dpas.
 11. The aluminoborosilicate glass of claim 10, having a viscosity temperature less than 1670° C. at 10² dPas.
 12. The aluminoborosilicate glass of claim 5, having a transformation temperature T_(g) of at least 700° C.
 13. The aluminoborosilicate glass of claim 5, having a transformation temperature T_(g) of at least 710° C.
 14. The aluminoborosilicate glass of claim 5, in which the CaO content is less than 6% by weight, but at least 4% by weight.
 15. The aluminoborosilicate glass of claim 5, in which the MgO content is less than 6% by weight.
 16. The aluminoborosilicate glass of claim 5, in which the MgO content is more than 0.5% by weight.
 17. The aluminoborosilicate glass of claim 5, in which the B₂O₃ content is less than 14% by weight.
 18. The aluminoborosilicate glass of claim 5, in which the SrO content is less than 0.02% by weight.
 19. An aluminoborosilicate glass having a density less than 2.40 g/cm³ and comprising the following components (in wt. %): SiO₂ 58-70 Al₂O₃ 12-20 B₂O₃  5-<14 MgO 0.5-6   CaO 4-6 BaO 0.1-5   SnO₂ 0-1 As₂O₃  0-2,

said glass, apart from random impurities, being free of SrO and free of alkali oxides; said glass further having a specific modulus of elasticity greater than 31 GPa·cm³·g⁻¹, a modulus of elasticity greater than 71 GPa, a viscosity temperature of less than 1320° C. at 10⁴ dPas, and a viscosity temperature of less than 1670° C. at 10² dPas. 